Vimium C is a browser extension that provides keyboard-driven navigation and productivity features, forked from Vimium. Its architecture is a classic Chrome/Firefox extension with a background service worker or page, content scripts injected into every page, and extension pages (options, omnibar, show image). The background script manages state, settings, browsing data (history, bookmarks), and orchestrates commands like tab management, URL opening, and synchronization. Content scripts implement the core user-facing features: link hints (detecting clickable elements and overlaying markers), keyboard key handlers with a finite state machine for mapping keystrokes to commands, visual mode for text selection, find-in-page, scrolling with smooth animations, and an omnibar (Vomnibar) for search, history, bookmarks, and command execution. The Vomnibar is a rich UI component that communicates with the background via port messaging. The extension supports multiple browsers (Chrome, Firefox, Edge) and both Manifest V2 and V3, with extensive version-specific conditionals and polyfills. The build system uses TypeScript, gulp, rollup, and terser to produce optimized builds, and includes custom patches to vendored TypeScript and Terser. The codebase demonstrates high engineering effort in handling complex browser quirks and performance optimization, but also carries technical debt from accumulated workarounds and legacy browser support.